- #1

Mithra

- 16

- 0

[itex]S = -\frac{1}{2}m^2\phi^2 - \frac{\lambda}{3!}\phi^3[/itex]

and the question then require drawing the feynman diagrams for the [itex]<\phi\phi>[/itex] at order [itex]\lambda^2[/itex].

I am told that there are 2 connected diagrams at one-loop order and one disconnected two-loop diagram and asked to draw them, however I am unsure what exactly defines which order of lambda a feynman diagram will be? As there is only a phi^3 in the action I believe this means that there can only be three-point interaction vertexes rather than four but I'm not sure if that's correct?

I think my connected diagrams are ok however for the two-loop diagram I initially had a single line connecting two points and then separately a point with two loops coming from it, however looking in the notes I see that that is a first order diagram (and also, possibly requires a phi^4 as there are four connections to the single point from the two loops?).

If anyone has any pointers as to what I should be looking for, or if I'm totally on the wrong track, that would be brilliant thanks!